The invention relates to an electric toothbrush which has a brush rod housed in the toothbrush casing in such a way to be rotatable, the brush rod being rotatable around its longitudinal axis by an electric motor with a rotating motor shaft by means of an eccentric pin which engages with a lever, the lever being securely fixed to the brush rod. Such an electric toothbrush is in general familiar and conventional.
The rotary motion of the motor is converted, in the familiar toothbrushes, into an oscillatory movement of the brush rod by means of a lever which is transversely aligned to the brush rod and which engages with an eccentric pin aligned parallel to the brush rod. Thus, a brush element placed on the brush rod moves in oscillatory motion accordingly. Recently this simple movement of the brush element has often been considered insufficient and a demand for a circling movement has arisen. For this movement, the brush rod must not only accomplish an oscillatory movement around its longitudinal axis but must also be moved simultaneously backwards and forwards in a lengthwise direction. To produce both of these superposed movements, relatively complicated gearing has been provided for the familiar toothbrushes up to the present so that the production of this sort of toothbrush is on the whole expensive.
The object of the invention is to construct a toothbrush of the type named at the beginning so that the rotary motion of its motor may be converted, with the most simple gearing as possible, into a simultaneous oscillatory and backwards and forwards movement.
The object is achieved in accordance with the invention in that the brush rod is, in addition, arranged so as to be slidable in axial direction and that the lever is axially parallel to the brush rod and the eccentric pin is perpendicular to the brush rod the eccentric pin gripping into a socket in the lever, the socket being in transverse direction to the brush rod.
This construction allows the eccentric cam to push the lever backwards and forwards with the brush rod, in the direction of the brush rod so that the desired axial shift of the brush rods takes place. Simultaneously, the eccentric cam causes on oscillatory movement of the lever to one side or the other when it moves in its orbit towards the sides. In this way, the two desired and superposed movements of the brush rod are achieved by means of a simple crank mechanism. Owing to the invention a very simple and therefore, reasonably priced toothbrush may be produced, the brush elements of which performing a circular movement which is advantageous for thorough cleaning of the teeth.
It is of particularly great advantage if a sliding member is positioned on the eccentric pin so as to be rotatable, the sliding member engaging with the socket and if both sides of the sliding member running axially parallel to the brush rod, and/or the corresponding sides of the socket, are curved or bevelled to enable an oscillatory movement of the lever. Such an arrangement operates with very little friction and may be produced at a reasonable price.
To enable the oscillatory movement of the lever, either the sides of the sliding member are convex or the sides of the socket in the lever, in contact with the sliding member, are concave. It is of course also possible for each of the contacting areas to be curved.
The toothbrush is structurally especially simple, in accordance with one advantageous embodiment of the invention, if the eccentric pin is provided on the face of a gear, this being transversely rotatable to the brush rod and housed in the toothbrush casing, whereby on the motor shaft, a pinion engages with the gear. The gear may, for example, be a bevel gear or a crown wheel. It is simply important that the motor shaft has a bell-crank drive so that the axis of the eccentric pin runs in transverse direction to the motor shaft and thus, in transverse direction to the brush rod.
The oscillatory movement of the lever is especially simple to produce, in accordance with another embodiment of the invention, if the part of the lever with the socket for the sliding member is of radial distance from the brush rod. This embodiment has a sliding member which engages with the lever at a considerable distance from the oscillatory axis of the lever, the oscillatory axis of the lever being the same as that of the brush rod. This results in a relatively great oscillatory momentum so that the oscillatory movement of the brush element occurs with great enough force.
Another embodiment is very space-saving if, according to this embodiment, the eccentric pin engages with the sliding member from the side of the brush rod.
Manually operated dental instruments are normally bent at the point where the handle begins. The brush element of an electric toothbrush may also have this bent form if, according to a further development of the invention, the gear is arranged in a front part of the toothbrush which bears the brush rod, the front part being rotatable and tiltable by means of a ball head and positioned in a ball cup in the handle of the toothbrush casing, the handle housing the motor. The centre of the ball head lies at the point of intersection of the gear axle and the motor shaft axle.
The gear allows for tilting of the front part of the toothbrush when necessary only around the gear axle due to the pinion engaging with the gear. To exclude forces on the gear and on the pinion, in an attempt to tilt the front part of the toothbrush into another direction, it is advantageous if the front part of the toothbrush has a support at each side of the axle which bears the gear, the support being in contact with a collar at the front of the handle. These supports prevent tilting into directions other than a direction transverse to the gear axle.
The possible direction of tilt of the front part of the toothbrush is clearly fixed if, according to another embodiment of the invention, the front part of the toothbrush is in contact with the collar at the front of the handle with a support area covering 180 degrees and if its tiltability is restricted by an inclined area adjoining this support area.
Another, very simple possibility of preventing the front part of the toothbrush from tilting into a direction which is not transverse to the gear axle is achieved when the gear axle protrudes out of the ball head on at least one side and engages with a bow-shaped groove in the handle.
The invention permits numerous embodiments. To clarify the basic principle of the invention further, an embodiment of the latter is represented in drawing and subsequently described.